In the field of “indoor” communications, wireless links are required to connect different devices in a house. For this, means for receiving and/or transmitting electromagnetic signals, or antennas, of the end-fire tapered slot type are used. Such antennas mainly constituted by a tapered slot realised on a metallic substrate are commonly called Vivaldi antennas or LTSA (Linear Tapered Slot Antenna). They can be integrated more easily into the devices because they radiate in the plane of the substrate. When several antennas of this type are used, for example in a network, the connection of the radiating device rapidly becomes complex.
The dimensioning of a Vivaldi antenna is well-known by those in the profession. It can be divided into three parts shown in FIG. 1, which are the dimensioning of the antenna A1 (Vivaldi profile), the dimensioning of the connection line 2 linked to a connection port P and the dimensioning of the line 2/slot F1 transition that enables the energy of line 2 to be transmitted to the antenna A1. To ensure the correct coupling of energy between the line 2 and the slot F1, it is necessary to obtain a position in specific geometrical conditions concerning the relative positions of the connection lines 2 and the slots F1 of the antennas A1. An example is given, for example, in the document U.S. Pat. No. 6,246,377.
There are two techniques for placing Vivaldi antennas A1 and A2 in a network. A first technique, shown in FIG. 2, involves connecting them in series by the same line 2. The length of line between the two line 2/slot F transitions determines the phase difference between the signals transmitted or received by two successive antennas A1 and A2. By taking an odd multiple of line length of the guided half-wavelength under the connection line realized for example according to the microstrip line technique, namely L=nLm/2 (n=2k+1, with k an integer), the transmitted fields E1 and E2 are symmetrical with respect to the axis of symmetry of the two antennas A1 and A2. For such a connection in series, the coupling to the antennas A1 and A2 is different from the point of view of the amplitude and the frequency phase difference. This is due to different line lengths between a connection port P and each of the antennas A1 and A2.
A second technique, shown in FIG. 3, consists of connecting them in parallel. The difference in length between L1 and L2 enables the phase difference between the transmitted fields E1 and E2 to be determined. By taking equal lengths, or such that |L1–L2|=n*Lm (where n is an integer), the transmitted fields E1 and E2 are as shown in FIG. 3. This connection technique gives a balanced connection but requires a more complex connection circuit. In particular, if the number of antennas increases, the dimensions of the connection network increase and its implementation sometimes requires the use of components. The cost of the structure consequently increases.
One solution, presented in document EP 0,301,216, is to replace the two line/slot transitions by a single line 2/slot FC transition by connecting the two slots together as shown in FIG. 4. There is therefore only a single line 2/slot FC transition and the slot FC terminates in an antenna, A1 and A2, at each of its two extremities. The coupled energy of the line 2 to the slot FC, is directed equally to the antennas A1 and A2.
However, such a radiating device has a fixed radiation pattern possessing, in particular, a null in the axis of symmetry of the antennas when the line 2 cuts the slot at an equal distance of A1 and A2. Such characteristics can prove to be very damaging within the framework of applications that require great isotropy in the radiating device.